An approach combining the high density of synthetic DNA arrays with high selectivity of spotted ones is proposed. It is based on a proprietary technology allowing rapid and affordable customization of the array sequences. Both synthetic and spotted DNA arrays have distinct advantages and problems. Synthetic arrays have higher density, allowing higher throughput. However, at present they can not be rapidly and cost- effectively customized. Spotted arrays usually have longer probes and therefore higher selectivity. They are much easier and cheaper to customize in a research laboratory. However, multi-point attachment of the probe to the substrate reduces the probe molecules' availability for binding, and possibly introduces a sequence-specific bias in quantitative assays. Besides, generating the probes for spotting is expensive and time-consuming. This proposal is aimed at combining the high density of synthetic arrays with the high selectivity and customization capability of the spotted ones. Electrowetting actuators for reagent delivery precisely position reagent droplets over the same area at each synthesis step. Therefore, the noise due to positional errors is inherently low, allowing an extremely low content of byproducts introduced per synthesis step. This will allow longer probes to be synthesized, bridging the gap between the two currently available array technologies. PROPOSED COMMERCIAL APPLICATIONS: Tools for genomics research and genetic testing are already a multimillion- dollar market, and rapidly growing. The unique advantages of the proposed technology may allow Nanolytics Company to become a major supplier of disposables and instruments for these applications. The ability to rapidly and affordably synthesize high-density DNA arrays in-house, offered to users by Nanolytics, will lead to market expansion.